Pressure measurements in human organs are an important source of information for diagnosing different states of illness. In the heart and blood vessel system, pressure measurements give information as to the pumping capacity of the heart, the closing and opening functions of the ventricles, constrictions and deposits in blood vessels, as well as deviations from the normal state in the peripheral network of blood vessels. Pressure measurements can also give valuable diagnostic information when applied to the different parts of the digestive system, from the throat to the anus. The state of urethras, spine as well as uterus is also diagnosed by pressure measurements, as well as several of the liquid filled body cavities such as the intracranial cavity, the spinal cord and the uterus.
Often both static pressure and dynamic pressure sequences are measured.
Conventional measurement techniques are based on hydraulic pressure transmission in liquid filled catheters between the measurement site and an externally placed pressure indicator. Such a system seldom manages to record pressure vibrations of a higher frequency than some tens of Hertz. The limitation is caused by the inertia of the liquid in combination with elastic components, which give rise to resonance phenomena. The properties are seldom completely stable but are drastically affected by such as the presence of microscopic air bubbles.
The problems discussed above can be solved by miniaturized pressure sensors which are applied directly to the measurement site, the measuring signal being transmitted via electrical or optical fibers. A number of examples of such arrangements have been published and these have also resulted in commercially available products (IEEE TRANSACTIONS ON BIO-MEDICAL ENGINEERING. Vol. BME-17, No. 3. p. 207-209, July 3, 1970, "MINIATURIZED PRESSURE TRANSDUCER INTENDED FOR INTRAVASCULAR USE" by Lars Lindstrom and DIGEST OF THE 11th INTERNATIONAL CONFERENCE ON MEDICAL AND BIOLOGICAL ENGINEERING-1976 OTTAWA, "DEVELOPMENT AND EVALUATION OF FIBER OPTIC PRESSURE CATHETER" by Saito and Masumoto, p. 690, and "30 th ACMB" LOS ANGELES, Nov. 5-9, 1977, "AN IMPROVED FIBEROPTIC CATHETER FOR INTRAVASCULAR PRESSURE AND SOUND MEASUREMENTS" p. 292 by French and Gerhard). Their clinical use has been extremely limited, however. The reason for this is primarily that the degree of miniaturization has not been sufficient. The commercially available sensors have an outer diameter of from 1.5 mm and upwards. This implies that clinical routines must be departed from, and in some cases a surgical operation will be necessary. Often, such complications can not be accepted, which has meant that the use of the miniaturized sensors has been very limited. Another important factor is the high price of the sensors, which is partly a consequence o their relatively complex fabrication, with a plurality of complicated elements, the assembly of which has often taken place using manual methods. The absence of functioning calibration routines is a further factor which has limited the spread of the miniaturized sensors.
The present invention provides a solution to these and associated problems, since it relates to the fabrication of a miniaturized pressure sensor which can have an exterior diameter of 0.5 mm. This allows the sensor to be used without needing to depart from established clinical routines. The sensor can be inserted through ordinary injection needles and catheters, even into narrow blood vessels and cavities. The sensor is manufactured with materials and methods adapted from semi-conductor technology, which results in a low cost. Manual and manipulative fabrication steps are replaced with the batch production of hundreds of elements at the same time. Furthermore, the small dimensions afford a practical solution to the calibration problems apparent from the Swedish patent 441 725.
The distinguishing features for the pressure sensor in accordance with the invention are disclosed in the accompanying claims.